1. Field of the Invention
The present invention generally relates to wireless communications and, in particular, to a method and apparatus for allocating a control channel of a relay node within a backhaul subframe in a wireless communication system.
2. Description of the Related Art
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique in which a serial input symbol stream is converted into parallel symbol streams and modulated into mutually orthogonal subcarriers, i.e., a plurality of subcarrier channels.
The multicarrier modulation-based system was first applied to military high-frequency radios in the late 1950s, and the OFDM scheme, which overlaps multiple orthogonal subcarriers, has been developing since 1970s. But there were limitations on its application to actual systems due to the difficulty in realization of orthogonal modulation between multiple carriers. However, the OFDM scheme has undergone rapid development since Weinstein et al. presented in 1971 that OFDM-based modulation/demodulation can be efficiently processed using DFT (Discrete Fourier Transform). In addition, as a scheme that uses a guard interval and inserts a Cyclic Prefix (CP) symbol into the guard interval, the negative influence of the system on multiple paths and delay spread has been reduced significantly.
Owing to such technical developments, OFDM technology is being widely applied to digital transmission technologies such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Wireless Local Area Network (WLAN), Wireless Asynchronous Transfer Mode (WATM), etc. That is, the OFDM scheme could not be widely used before due to its high hardware complexity, but the development of various digital signal processing technologies including Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT) has facilitated its realization.
In the meantime, an LTE-A system can include relay nodes as well as base stations (evolved Node B, eNodeB, or eNB) and mobile stations (User Equipment, or UE). A base station can allocate transmission resources for the backhaul link between the base station and the relay node and the resources allocated for the backhaul link are referred to as backhaul subframes.
FIGS. 1 and 2 are diagrams illustrating a principle for configuring a backhaul subframe for the relay nodes in an LTE-A system.
Referring to FIGS. 1 and 2, reference number 343 denotes a region in which the control channel of a relay node is transmitted. The region 343 is a resource informed by higher layer signaling. The allocated resource amount, i.e. the size of Resource Block (RB) 401, is semi-static, and the RB used in actual transmission may change in every backhaul subframe.
In the case where the control channel of the relay node is transmitted in the allocated control region by imitating the control channel structure of an LTE system, the resource amount for transmission is less than (but not equal to) the allocated resource and, as a consequence, a blank area, as denoted by reference number 331, in which no transmission occurs is distributed across the entire control channel, resulting in waste of resource. Although, in the case where the resource is allocated semi-statically, the region allocated for the relay node varies every subframe, the resource is not easily changed in size and is indicated fixedly, such that it is difficult to allocate resources in a frequency selective manner. The frequency selective resource allocation can be performed for the data channel for transmission to other terminals within the cell as well as the relay resource. In the case where the relay resource region is pre-configured in a large size for this, the relay must perform a plurality of blind decodings, resulting in an increase of relay implementation complexity. In order to perform the frequency selective resource allocation, the relay node must inform a large amount of the semi-static resource 415, resulting in increase in the number of blind decodings. In the case where the large amount of the semi-static resource is informed, the number of unnecessary blind decodings also increases especially when a small transmission resource is allocated, resulting in degradation of efficiency.